If you do not specify filename the script will look for a
file named annotated_prs.txt in the public_html
directory owned by username.

The input format is fairly free-form: any line that starts with a numeric
is magically assumed to be a PR number; otherwise it is simply copied to
the output. A line starting with %QUERY_PR [parameters] is
interpreted a a command to be fed directly to GNATS.

The output is written to filename except with
.html substituted for .txt.